1. Field of the Invention
The present invention relates to control signal distribution for T/R (transmitter/receiver) modules of a phased-array antenna, and more particularly to a control-signal distribution system for densely packaged T/R modules of a phased-array antenna.
2. Discussion of the Background
Phased-array antennas for use in smaller aircraft must of necessity be small. In order to achieve the required antenna performance with a small antenna, it is necessary to operate at a high radio frequency (e.g., X-band) and to employ a large number of radiating elements and associated T/R modules. The small antenna size and the large number of T/R modules are reflected in the packaging density. Under these conditions, it is difficult to effectively distribute control signals in such dense phased-array antennas with existing hardware. For example, hardwired signal interfaces to the modules are impractical because it is difficult to make reliable connections to a large number of T/R modules without causing excessive crosstalk between power and data conductors.
Optical data distribution technology is known to have a potential to solve these problems. For example, the optical data transmission path which carries the control-signal lends itself to being reliably connected to the input of the phased-array antennas. Although optical data distribution technology has been applied successfully to large size, low frequency, phased-array antennas (e.g., AST surveillance antennas), it has not been successfully applied to small-size, high-frequency, phased-array antennas having a large number of miniaturized T/R modules because the small-size, high-frequency antennas require high packaging density. Thus, the space available for accommodating signal distribution is extremely limited. This large number of miniaturized T/R modules typically requires closer spacing between the modules than does the large-size, low-frequency, phased-array antennas.
In dense/packed phased-array antennas, it is further required that control-signal highways which terminate within each T/R module should be efficient in terms of optical energy transfer ratio for signal delivery to the T/R module. For example, the BER (Bit Error Rate) for the control-signal at each T/R module should be better than 10.sup.-9. This in turn demands uniform optical energy distribution to each T/R module and efficient coupling of the optical energy across air gaps with low sensitivity to positional tolerances. At present, this type of optical energy distribution is not achievable in small-size, high-frequency, phased-array antennas.